(1) Field of the Invention
This invention relates to a packet transmission apparatus, a packet forwarding method, and a packet transmission system. More particularly, this invention relates to a packet transmission apparatus, a packet forwarding method, and a packet transmission system, which transmits packets with a Resilient Packet Ring (RPR) network as a backbone, the RPR supporting bandwidth sharing on a ring.
(2) Description of the Related Art
As a communication backbone for wide-area networks enabling long-distance transmission, Synchronous Optical NETwork/Synchronous Digital Hierarchy (SONET/SDH)-based ring networks are mainly used. In recent years, however, a technology called an RPR has been a focus of attention as an alternative of SONET/SDH.
The RPR is a new Media Access Control (MAC) transmission technology being standardized by the IEEE802.17 working group, and realizes a high-reliable dual packet ring network that enables swift switching independent of layer 1 (an existing technology is employed for the layer 1). In addition, with spatial reuse that allows bandwidth sharing among separated desired zones, the RPR can increase ring bandwidth availability.
The RPR technology enables transmitting IEEE802.17 MAC frames (RPR frames) to a ring network by using a physical layer of layer 1 including a transmission rate system for SONET Optical Carrier (OC)-n or SDH synchronous Transport Module (STM)-n, or 10 GbE (enables RPR over SONET/SDH, RPR over GBE, etc.).
The IEEE802.17 does not provide a specification for processing Virtual Local Area Network (VLAN) protocols at the RPR layer. Therefore, an RPR node cannot process such VLAN protocols at the RPR layer but has to process an incoming VLAN packet at the MAC layer that is higher than the RPR layer.
In a case where an RPR is used as a relay network of a VLAN using a VLAN protocol, each RPR node receives all packets going around the ring and always passes the all packets from the RPR layer to the MAC layer to check the VLAN identifiers (VLAN IDs) of the packets.
Then the RPR node determines whether each packet has the VLAN ID of a VLAN to which the own node belongs, in order to determine whether to receive or destroy the VLAN packet. That is, each node should check all packets from the ring at the MAC layer to see whether to take in and process the packets. In order to check the all packets without fail, the MAC layer should have capability of processing packets within the RPR bandwidth.
As a conventional VLAN technique, there has been proposed a technique of realizing group communication by transmitting a frame having set therein an own group address and a transmission destination terminal identifier (for example, refer to Japanese Unexamined Patent Publication No. 2003-143178 (paragraphs [0012]-[0014], FIG. 1)).
FIG. 21 shows a configuration of an RPR VLAN where an RPR is used as a VLAN relay network. The RPR VLAN 100 comprises five RPR nodes N1 to N5 and terminals t1 to t10.
The node N1 is connected to the terminals t1 and t2, the node N2 to the terminals t3 and t4, the node N3 to the terminals t5 and t6, the node N4 to the terminals t7 and t8, and the node N5 to the terminals t9 and t10.
In addition, on the network, there are tree VLANs 1, 2, and 3. Out of the RPR nodes N1 to N5, the nodes N1, N2 and N3 belong to the VLAN 1, the nodes N3, N4, and N5 belong to the VLAN 2, and the nodes N1, N2, N4 and N4 belong to the VLAN 3.
These combinations are determined depending on which VLANs the terminals connected to own nodes belong to.
Now, the VLAN 1 will be described by way of example. It is assumed that the terminal t1, which belongs to the VLAN 1 and is connected to the node N1, transmits a packet with VLAN ID=1, and the node N1 receives and transmits this packet with VLAN ID=1 to the RPR ring. The node N1 converts the VLAN packet with the VLAN ID of the VLAN 1 into an RPR packet and transmits this RPR packet clockwise (to the east side). At this time the node N1 stores an own MAC address as a transmission source address in the RPR packet. It should be noted that the RPR packet may be transmitted counterclockwise (to the west side).
The RPR packet transmitted to the ring is received by the node N2. Since a VLAN ID cannot be identified at the RPR layer in IEEE802.17 RPR technology, the node N2 processes the RPR packet at the MAC layer, and also forwards the RPR packet to the node N3 in the east direction.
The node N2 first checks the VLAN ID at the MAC layer, and if the own node belongs to a VLAN identified by the VLAN ID, takes in the packet, and forwards the packet to terminals based on MAC learning of the MAC layer. On the other hand, the node N3 receiving the RPR packet from the node N2 operates in the same manner as the node N2.
Each of the nodes N4 and N5 receives the RPR packet on the ring similarly. The node N4, N5 takes the packet into the own node and checks the VLAN ID of the packet at the MAC layer. Since the nodes N4 and N5 do not belong to the VLAN 1, the node N4, N5 destroys the packet with VLAN ID=1 at the MAC layer.
Simultaneously, the node N4, N5 transmits the RPR packet to the east side. After going around the ring, the RPR packet transmitted from the node N1 returns to the node N1. Since the node N1 recognizes that the RPR packet has the own node address as the transmission source address and therefore the RPR packet was originally transmitted by the own node, the node N1 does not transmit the packet to the ring but destroys the RPR packet, thereby preventing the RPR packet from circulating the ring again.
As described above, in the IEEE802.17 RPR technology, the VLAN ID of a VLAN cannot be identified at the RPR layer, so that each RPR node necessarily passes an incoming packet from the RPR layer to the MAC layer in order to check the VLAN ID of the VLAN packet.
Therefore, such a conventional RPR technology, in a case of a ring bandwidth of 10 Gbps, the MAC layer of an RPR node requires packet processing capability for 10 Gbps, which is equal to the ring bandwidth, even if packets to be processed in a relevant VLAN are less than 1 Gbps, which increases processing loads on the MAC layer and also increases cost due to over specification.
Further, a VLAN packet necessarily goes around the ring and is removed from the ring by a transmission source RPR node, which causes the packet to pass through unnecessary nodes, resulting in wasting ring bandwidth.
In the above example, since only the RPR nodes N1, N2 and N3 belong to the VLAN 1, the packet with VLAN ID=1 transmitted from the node N1 to the east side may not be forwarded to the nodes N4 and N5. That is to say, from an east side point of view, the packet unnecessarily goes through zones between the nodes N3 and N4, between the nodes N4 and N5 and between the nodes N5 and N1. This wastes the ring bandwidth.